/* ============================================================
   TreadmillCalc — native CSS, no framework
   ============================================================ */

:root {
  --bg: #f6f8f7;
  --surface: #ffffff;
  --surface-2: #f1f4f3;
  --text: #0f1a17;
  --text-muted: #5d6b67;
  --border: #e4e9e7;
  --primary: #10b981;
  --primary-glow: rgba(16,185,129,.35);
  --flame: #f97316;
  --flame-glow: rgba(249,115,22,.35);
  --shadow: 0 10px 30px -12px rgba(15,26,23,.15);
  --radius: 16px;
  --radius-sm: 10px;
  --gradient-primary: linear-gradient(135deg,#10b981,#06b6d4);
  --gradient-flame: linear-gradient(135deg,#f97316,#ef4444);
  --gradient-hero: radial-gradient(ellipse at top, rgba(16,185,129,.14), transparent 60%);
}

[data-theme="dark"] {
  --bg: #0b1411;
  --surface: #121d1a;
  --surface-2: #18241f;
  --text: #ecf3f0;
  --text-muted: #95a39d;
  --border: rgba(255,255,255,.08);
  --primary: #34d399;
  --primary-glow: rgba(52,211,153,.45);
  --flame: #fb923c;
  --flame-glow: rgba(251,146,60,.45);
  --shadow: 0 20px 50px -20px rgba(0,0,0,.6);
  --gradient-primary: linear-gradient(135deg,#34d399,#22d3ee);
  --gradient-flame: linear-gradient(135deg,#fb923c,#f43f5e);
  --gradient-hero: radial-gradient(ellipse at top, rgba(52,211,153,.18), transparent 60%);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  transition: background .3s, color .3s;
  background-image: var(--gradient-hero);
  background-repeat: no-repeat;
  background-size: 100% 600px;
}

.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }

/* ---------- Topbar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  backdrop-filter: blur(14px);
  background: color-mix(in srgb, var(--bg) 75%, transparent);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 20px;
}
.brand { display: flex; align-items: center; gap: 12px; }
.brand-mark {
  width: 40px; height: 40px; border-radius: 12px;
  display: grid; place-items: center; color: white;
  background: var(--gradient-primary);
  box-shadow: 0 0 30px var(--primary-glow);
}
.brand-mark svg { width: 22px; height: 22px; }
.brand-name { font-weight: 700; font-size: 16px; letter-spacing: -.01em; }
.brand-sub { font-size: 12px; color: var(--text-muted); }

.topbar-actions { display: flex; align-items: center; gap: 10px; }
.unit-toggle {
  display: inline-flex; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: 999px; padding: 4px;
}
.unit-btn {
  border: 0; background: transparent; color: var(--text-muted);
  padding: 6px 14px; border-radius: 999px; font-size: 13px; font-weight: 600;
  cursor: pointer; transition: all .2s;
}
.unit-btn.active {
  background: var(--surface); color: var(--text);
  box-shadow: 0 1px 3px rgba(0,0,0,.08);
}
.icon-btn {
  width: 40px; height: 40px; border-radius: 12px;
  background: var(--surface-2); border: 1px solid var(--border);
  display: grid; place-items: center; cursor: pointer; color: var(--text);
  transition: all .2s;
}
.icon-btn:hover { background: var(--surface); box-shadow: var(--shadow); }
.icon-btn svg { width: 18px; height: 18px; }
.icon-sun { display: none; }
.icon-moon { display: block; }
[data-theme="dark"] .icon-sun { display: block; }
[data-theme="dark"] .icon-moon { display: none; }

/* ---------- Hero ---------- */
.hero { text-align: center; padding: 60px 0 40px; }
.eyebrow {
  display: inline-block; font-size: 12px; font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: var(--primary);
  padding: 6px 14px; border-radius: 999px;
  background: color-mix(in srgb, var(--primary) 12%, transparent);
  border: 1px solid color-mix(in srgb, var(--primary) 25%, transparent);
}
.hero-title {
  font-size: clamp(34px, 6vw, 56px); font-weight: 800;
  letter-spacing: -.03em; margin: 20px 0 12px;
  background: var(--gradient-primary);
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
}
.hero-sub { color: var(--text-muted); max-width: 640px; margin: 0 auto; font-size: 17px; }

/* ---------- Cards ---------- */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
}

/* ---------- Calculator grid ---------- */
.grid-main {
  display: grid; gap: 20px; margin-top: 30px;
  grid-template-columns: 1fr;
}
@media (min-width: 900px) {
  .grid-main { grid-template-columns: 1.05fr 1.2fr; }
}

.panel-header h2 { margin: 0 0 4px; font-size: 20px; }
.muted { color: var(--text-muted); font-size: 14px; margin: 0; }

.field { margin-top: 22px; }
.field.inline { display: flex; align-items: center; gap: 12px; margin-top: 14px; }
.field.inline label { margin: 0; }
.field label {
  display: block; font-size: 13px; font-weight: 600;
  color: var(--text-muted); margin-bottom: 8px;
}
.field .unit { color: var(--text-muted); font-weight: 400; }
.field-head { display: flex; align-items: center; justify-content: space-between; margin-bottom: 8px; }
.value-chip {
  font-weight: 700; font-size: 14px;
  padding: 4px 10px; border-radius: 8px;
  background: var(--surface-2); color: var(--text);
  font-variant-numeric: tabular-nums;
}
input[type="number"] {
  width: 100%; padding: 12px 14px; font-size: 15px;
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  background: var(--surface-2); color: var(--text);
  font-family: inherit; transition: all .2s;
}
input[type="number"]:focus {
  outline: none; border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--primary-glow);
}

/* Range slider */
input[type="range"] {
  -webkit-appearance: none; appearance: none;
  width: 100%; height: 6px; border-radius: 999px;
  background: var(--surface-2); cursor: pointer;
}
input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none; appearance: none;
  width: 20px; height: 20px; border-radius: 50%;
  background: var(--gradient-primary);
  border: 3px solid var(--surface);
  box-shadow: 0 0 16px var(--primary-glow);
  cursor: pointer; transition: transform .15s;
}
input[type="range"]::-webkit-slider-thumb:hover { transform: scale(1.15); }
input[type="range"]::-moz-range-thumb {
  width: 20px; height: 20px; border-radius: 50%;
  background: var(--primary); border: 3px solid var(--surface);
  cursor: pointer;
}

.presets { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 10px; }
.preset {
  border: 1px solid var(--border); background: var(--surface-2);
  color: var(--text-muted); padding: 6px 12px; border-radius: 999px;
  font-size: 12px; font-weight: 600; cursor: pointer; transition: all .15s;
  font-family: inherit;
}
.preset:hover { color: var(--text); border-color: var(--primary); }
.preset.active {
  background: var(--primary); color: white; border-color: var(--primary);
}

/* ---------- Results ---------- */
.results { display: flex; flex-direction: column; gap: 20px; }
.result-hero {
  background: var(--gradient-flame); color: white;
  border: 0; position: relative; overflow: hidden;
  box-shadow: 0 20px 60px -20px var(--flame-glow);
}
.result-hero::after {
  content: ""; position: absolute; inset: 0;
  background: radial-gradient(circle at 80% 20%, rgba(255,255,255,.25), transparent 60%);
  pointer-events: none;
}
.result-label { font-size: 13px; font-weight: 600; opacity: .9; text-transform: uppercase; letter-spacing: .08em; }
.result-big {
  font-size: clamp(48px, 8vw, 72px); font-weight: 800;
  letter-spacing: -.03em; line-height: 1; margin: 8px 0;
  font-variant-numeric: tabular-nums;
}
.result-big .unit-sm { font-size: .35em; font-weight: 600; opacity: .85; margin-left: 6px; }
.result-meta { display: flex; gap: 10px; opacity: .9; font-size: 14px; font-weight: 500; }
.dot { opacity: .5; }

.result-grid { display: grid; gap: 14px; grid-template-columns: repeat(2, 1fr); }
@media (min-width: 600px) { .result-grid { grid-template-columns: repeat(4, 1fr); } }
.stat { padding: 18px; }
.stat-label { font-size: 12px; font-weight: 600; color: var(--text-muted); text-transform: uppercase; letter-spacing: .08em; }
.stat-value {
  font-size: 28px; font-weight: 800; margin-top: 4px;
  font-variant-numeric: tabular-nums; letter-spacing: -.02em;
}
.stat-value .unit-sm { font-size: 14px; font-weight: 600; color: var(--text-muted); }
.stat-foot { font-size: 12px; color: var(--text-muted); margin-top: 4px; }

/* ---------- Tabs ---------- */
.tabs-card { margin-top: 24px; }
.tabs {
  display: flex; gap: 4px; padding: 4px;
  background: var(--surface-2); border-radius: 12px;
  margin-bottom: 20px; overflow-x: auto;
}
.tab {
  flex: 1; min-width: 120px; border: 0; background: transparent;
  color: var(--text-muted); padding: 10px 16px; border-radius: 8px;
  font-size: 13px; font-weight: 600; cursor: pointer; font-family: inherit;
  transition: all .2s; white-space: nowrap;
}
.tab.active { background: var(--surface); color: var(--text); box-shadow: 0 1px 3px rgba(0,0,0,.08); }
.tab-panel { display: none; }
.tab-panel.active { display: block; animation: fade .25s ease; }
.tab-panel h3 { margin: 0 0 4px; font-size: 18px; }
@keyframes fade { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; transform: none; } }

#chart {
  width: 100%; height: 240px; margin-top: 16px;
  display: block;
}

.table-wrap { margin-top: 16px; overflow-x: auto; }
table { width: 100%; border-collapse: collapse; font-size: 14px; }
th, td { padding: 12px 14px; text-align: left; border-bottom: 1px solid var(--border); }
th { font-size: 12px; font-weight: 600; color: var(--text-muted); text-transform: uppercase; letter-spacing: .06em; }
tbody tr { transition: background .15s; }
tbody tr:hover { background: var(--surface-2); }
tbody tr.active { background: color-mix(in srgb, var(--primary) 12%, transparent); }
td { font-variant-numeric: tabular-nums; }

.zones { display: flex; flex-direction: column; gap: 10px; margin-top: 16px; }
.zone {
  display: grid; grid-template-columns: 1fr auto; gap: 10px;
  padding: 14px 16px; border-radius: 12px;
  background: var(--surface-2); border: 1px solid var(--border);
  align-items: center;
}
.zone-name { font-weight: 600; font-size: 14px; }
.zone-desc { font-size: 12px; color: var(--text-muted); }
.zone-bpm { font-weight: 700; font-variant-numeric: tabular-nums; font-size: 15px; }
.zone-bar { grid-column: 1 / -1; height: 6px; border-radius: 999px; background: var(--surface); overflow: hidden; }
.zone-bar > span { display: block; height: 100%; border-radius: 999px; }

/* ---------- SEO Content Section ---------- */
.seo-section { margin-top: 24px; }
.seo-section h2 {
  font-size: clamp(22px, 3.5vw, 28px); font-weight: 800;
  letter-spacing: -.02em; margin: 32px 0 12px;
}
.seo-section h2:first-child { margin-top: 0; }
.seo-section h3 {
  font-size: 17px; font-weight: 700; margin: 24px 0 8px;
  color: var(--text);
}
.seo-section p {
  color: var(--text-muted); font-size: 15px; line-height: 1.7;
  margin: 0 0 14px;
}
.seo-section p strong { color: var(--text); }
.seo-section ul {
  padding-left: 20px; margin: 0 0 16px;
}
.seo-section ul li {
  color: var(--text-muted); font-size: 15px; line-height: 1.7;
  margin-bottom: 10px;
}
.seo-section ul li strong { color: var(--text); }
.seo-section .formula {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 14px 18px;
  font-size: 14px;
  overflow-x: auto;
  margin: 10px 0 16px;
}
.seo-section .formula code {
  background: transparent;
  padding: 0;
  font-size: 14px;
  color: var(--text);
}
.seo-section code {
  background: color-mix(in srgb, var(--primary) 10%, transparent);
  color: var(--primary);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: .95em;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
}
.seo-section em { color: var(--text-muted); font-size: 14px; }

/* Block diagram — CSS flexbox replacement for ASCII art */
.diagram {
  display: flex; flex-direction: column; align-items: center; gap: 10px;
  margin: 16px 0 24px; padding: 24px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.diagram-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 18px;
  font-size: 13px; font-weight: 700;
  text-align: center;
  color: var(--text);
  box-shadow: 0 2px 8px rgba(0,0,0,.04);
}
.diagram-box.primary {
  background: var(--gradient-primary);
  color: white; border: 0;
  font-size: 14px; padding: 12px 24px;
  box-shadow: 0 10px 30px -10px var(--primary-glow);
}
.diagram-box.detail {
  font-weight: 500; font-size: 12px;
  color: var(--text-muted); padding: 10px 14px;
  line-height: 1.5;
}
.diagram-arrow {
  font-size: 18px; color: var(--text-muted);
  line-height: 1;
}
.diagram-row {
  display: grid; gap: 12px;
  grid-template-columns: 1fr;
  width: 100%; max-width: 720px;
}
@media (min-width: 640px) {
  .diagram-row { grid-template-columns: repeat(3, 1fr); }
}
.diagram-col {
  display: flex; flex-direction: column; gap: 8px;
}

.footer {
  text-align: center; padding: 40px 0 60px;
  color: var(--text-muted); font-size: 13px;
}

/* ============================================================
   Navigation + Footer (multi-page)
   ============================================================ */
.primary-nav {
  display: flex; align-items: center; gap: 4px;
  margin-left: 24px;
}
.primary-nav a {
  position: relative;
  text-decoration: none;
  color: var(--text-muted);
  font-size: 14px; font-weight: 600;
  padding: 8px 14px;
  border-radius: 10px;
  transition: color .2s, background .2s;
}
.primary-nav a:hover { color: var(--text); background: var(--surface-2); }
.primary-nav a.active {
  color: var(--text);
  background: color-mix(in srgb, var(--primary) 14%, transparent);
}
.primary-nav a.active::after {
  content: ""; position: absolute; left: 14px; right: 14px; bottom: 4px;
  height: 2px; border-radius: 2px; background: var(--gradient-primary);
}

.nav-toggle {
  display: none;
  width: 40px; height: 40px; border-radius: 12px;
  background: var(--surface-2); border: 1px solid var(--border);
  color: var(--text); cursor: pointer;
  align-items: center; justify-content: center;
}
.nav-toggle svg { width: 20px; height: 20px; }

.topbar-left { display: flex; align-items: center; }

@media (max-width: 760px) {
  .primary-nav {
    position: absolute; top: 100%; left: 0; right: 0;
    flex-direction: column; align-items: stretch;
    gap: 2px; margin: 0; padding: 12px 16px;
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow);
    transform: translateY(-8px); opacity: 0; pointer-events: none;
    transition: opacity .2s, transform .2s;
  }
  .primary-nav.open { transform: none; opacity: 1; pointer-events: auto; }
  .primary-nav a { padding: 12px 14px; }
  .primary-nav a.active::after { display: none; }
  .nav-toggle { display: inline-flex; }
  .topbar { position: relative; }
}

/* ---------- Modern footer ---------- */
.site-footer {
  margin-top: 60px;
  border-top: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface) 60%, transparent);
}
.site-footer-inner {
  display: grid; gap: 24px;
  grid-template-columns: 1fr;
  padding: 40px 20px 28px;
}
@media (min-width: 720px) {
  .site-footer-inner { grid-template-columns: 1.4fr 1fr; align-items: start; }
}
.footer-brand { display: flex; align-items: center; gap: 12px; }
.footer-tag { color: var(--text-muted); font-size: 14px; margin: 10px 0 0; max-width: 380px; }
.footer-links {
  display: flex; flex-wrap: wrap; gap: 6px 4px;
  justify-content: flex-start;
}
@media (min-width: 720px) { .footer-links { justify-content: flex-end; } }
.footer-links a {
  text-decoration: none; color: var(--text-muted);
  font-size: 14px; font-weight: 500;
  padding: 6px 12px; border-radius: 8px;
  transition: color .2s, background .2s;
}
.footer-links a:hover { color: var(--text); background: var(--surface-2); }
.footer-bottom {
  border-top: 1px solid var(--border);
  padding: 16px 20px;
  text-align: center;
  color: var(--text-muted); font-size: 13px;
}

/* ============================================================
   Static content pages (about, contact, privacy, disclaimer)
   ============================================================ */
.page {
  max-width: 820px; margin: 40px auto 0;
}
.page .page-eyebrow {
  display: inline-block; font-size: 12px; font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: var(--primary);
  padding: 6px 14px; border-radius: 999px;
  background: color-mix(in srgb, var(--primary) 12%, transparent);
  border: 1px solid color-mix(in srgb, var(--primary) 25%, transparent);
}
.page h1 {
  font-size: clamp(32px, 5vw, 44px); font-weight: 800;
  letter-spacing: -.025em; margin: 18px 0 10px;
  background: var(--gradient-primary);
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent;
}
.page .lead {
  color: var(--text-muted); font-size: 17px; margin: 0 0 28px;
}
.prose { padding: 32px; }
.prose h2 {
  font-size: 20px; font-weight: 700;
  margin: 28px 0 10px;
}
.prose h2:first-child { margin-top: 0; }
.prose p, .prose li {
  color: var(--text); font-size: 15px; line-height: 1.7;
}
.prose p { margin: 0 0 14px; color: var(--text-muted); }
.prose ul { padding-left: 20px; margin: 0 0 16px; }
.prose ul li { margin-bottom: 6px; color: var(--text-muted); }
.prose strong { color: var(--text); }
.prose .updated {
  font-size: 13px; color: var(--text-muted);
  padding: 8px 12px; border-radius: 8px;
  background: var(--surface-2);
  display: inline-block; margin-bottom: 20px;
}

/* Contact form */
.contact-grid {
  display: grid; gap: 20px;
  grid-template-columns: 1fr;
}
@media (min-width: 880px) { .contact-grid { grid-template-columns: 1.2fr 1fr; } }
.contact-info { display: flex; flex-direction: column; gap: 14px; padding: 28px; }
.contact-info h3 { margin: 0; font-size: 16px; }
.contact-info p { margin: 0; color: var(--text-muted); font-size: 14px; }
.info-row {
  display: flex; gap: 12px; align-items: flex-start;
  padding: 12px; border-radius: 12px; background: var(--surface-2);
}
.info-row svg { width: 18px; height: 18px; color: var(--primary); flex-shrink: 0; margin-top: 2px; }
.info-row b { display: block; font-size: 13px; margin-bottom: 2px; }

form.contact-form { padding: 28px; display: flex; flex-direction: column; gap: 16px; }
form.contact-form label {
  display: block; font-size: 13px; font-weight: 600;
  color: var(--text-muted); margin-bottom: 6px;
}
form.contact-form input,
form.contact-form textarea {
  width: 100%; padding: 12px 14px; font-size: 15px;
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  background: var(--surface-2); color: var(--text);
  font-family: inherit; transition: all .2s;
  resize: vertical;
}
form.contact-form input:focus,
form.contact-form textarea:focus {
  outline: none; border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--primary-glow);
}
.btn-primary {
  border: 0; cursor: pointer; font-family: inherit;
  background: var(--gradient-primary); color: white;
  font-weight: 700; font-size: 15px;
  padding: 13px 22px; border-radius: var(--radius-sm);
  box-shadow: 0 10px 30px -10px var(--primary-glow);
  transition: transform .15s, box-shadow .2s;
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 14px 40px -10px var(--primary-glow); }
.form-status {
  font-size: 14px; color: var(--primary); font-weight: 600;
  min-height: 20px;
}